The Antikythera Mechanism is a device consisting of approximately 37 gears of remarkable sophistication believed to have been constructed at some point between 150 and 100 bce

The front side of the device contains a 365-day dial which accurately charts the positions of the Sun, moon, the five other planets known to the Greeks at the time, and the Zodiac. It is believed that a half-silvered ball in the moon dial would depict the phases of the moon. It is important to note that although the device was built according to a geocentric model – that is, with Earth at the center of the universe – it still charts the location of the planets accurately. Even though their general beliefs about the nature of the solar system were incorrect, they were still able to develop sophisticated mathematical models to explain the motions of the planets.

The other side of the device has two main dials. One of them depicts the 19-year Metonic Cycle, which is the period of time in which the solar year and the lunar month sync up. The other dial shows the Saros cycle, an approximately 18-year cycle used to predict the occurrence of eclipses. A third, smaller dial was recently uncovered on the device depicting a four-year cycle, used to show during which years Olympic games would take place.

The device is powered by a crank or knob on the side, which drives all the internal machinery in perfect synchronization. One can easily imagine the importance of such a device in an age when great meaning was still placed on the positions of the planets. The device is believed to have been inscribed with a sort of “instruction manual”, indicating that it was built to be used by people other than the scientific elite of the time, making this in many ways the first “personal computer”.